1. Field of the Invention
The invention relates to the construction and installation of a loading dock leveler, namely a pivotable platform for bridging between the different elevations of a loading dock slab or similar structure, and a vehicle cargo bed. In particular, a loading dock leveler mechanism is mountable in a precast concrete box insert that has facilities for attachment of the mechanism and for engagement with a poured concrete slab forming the balance of the loading dock or other floor or platform.
2. Prior Art
A loading dock provides a surface for loading and unloading cargo and the like from an elevation substantially equal to that of the cargo bed of a vehicle, for example, a semitrailer, railroad car, etc. Unfortunately, the cargo beds of vehicles are not all at the same elevation. When a truck backs up to a loading dock there is often a step up or down from the dock to the cargo bed or vice versa. The step interferes with loading and unloading, and can be a trip hazard as well as an obstruction that makes it difficult to slide or roll cargo, a handtruck or another vehicle from one elevation to the other. To solve this problem, a dock leveler can be provided and positioned so that the forward edge of a movable platform rests on the cargo bed and provides a ramp forming a stepless transition between the two elevations.
A loading dock leveler typically comprises a mechanism mounted in an indentation or pit on the top of a loading dock or other slab, floor or similar structure. A typical loading dock or slab has a horizontal surface at a given elevation and a vertical front face. The indentation opens upwardly and forwardly at the vertical front face of the loading dock or slab. The mechanism includes a movable platform that is hinged on a horizontal axis at the upper rear edge of the indentation or pit. Powered means are provided for pivoting the platform up or down from a position at which the platform is flush with the surface of the slab. The powered means can be a pneumatic or hydraulic cylinder, an inflatable body or a motor, etc., bearing between the bottom of the indentation and the underside of the movable platform.
Examples of dock levelers are disclosed, for example, in U.S. Pat. No. 4,110,860--Neff et al.; U.S. Pat. No. 4,570,277--Hahn et al.; U.S. Pat. No. 4,928,340--Alexander; and U.S. Pat. No. 5,442,825--Hahn et al. Each of these examples includes a movable platform that advantageously fits closely in an indentation. Any gap between the platform and the edges of the indentation at either side provides a path for material to drop below the platform and rest in the indentation where it potentially can interfere with positioning of the platform. Such material may be difficult or dangerous to remove. The gap also allows ingress for dirt and water. Collapsible vertical side skirts are provided in Neff and Alexander to block material from passing horizontally under the platform when the platform is raised above the surface of the dock slab. In Hahn '825, a compressible edge seal protrudes horizontally to engage against the side walls of the indentation. The seal corrects for a gap between the platform and the dock slab, but only when the platform is lowered below the surface of the slab and into the indentation.
Loading dock slabs are constructed to receive leveler mechanisms, i.e., the loading dock slab is provided with an indentation during construction. If the indentation is not provided when the slab is built, a section of the slab must be demolished and rebuilt to retrofit a leveler mechanism. Building a slab with an indentation involves building forms of the necessary size to complement the dimensions of the mechanism, pouring the slab around the forms and smoothing the horizontal surface of the indentation to make a smooth rectilinear pit.
Leveler mechanisms typically include a frame that is adapted to rest on the bottom of the indentation or pit. Angle iron bars can be set around the perimeter edges of the indentation, either being parts of the leveler frame or independently mounted. Preferably such angle iron bars are inset when forming the slab so as to be flush with the slab horizontal surface as well as with the vertical side walls of the pit. Similarly, an angle iron bar which can be separate or part of the base frame overlaps the front edge of the indentation, extending downward over the front wall of the dock. In Hahn '277, the frame also includes angle iron sections that rest against the side walls at the lower corners of the pit, presumably protecting against rocking of the movable platform. Finally, resilient bumpers are mounted on the vertical front face of the dock slab so that a truck can be backed to a fixed position relative to the dock slab.
A dock leveler is preferably a robust structure. However, it would be advantageous if the dimensions of the dock leveler could also be more positionally accurate and precise. What is needed is a way to improve the fit and alignment of the leveler mechanism with the walls of the pit, and to do so without relying on the already considerable craftsmanship needed to form the indented dock slab.